The present invention relates to a new and improved method of, and apparatus for, false-twist spinning.
Generally speaking, the apparatus of the present method, is of the type comprising a sliver feed unit or feeder, such as, by way of example, a drafting arrangement or mechanism, which forms a nip line or nip for an outfed sliver and which is operative to deliver the sliver at a predeterminate width from the nip line. There are also provided spinning means which comprise suction means for engaging and conveying or transporting fiber ends of the fibers delivered by the sliver feed unit or feeder and therefore forwarding or conveying the thus engaged fibers. These engaged fiber ends constitute front or leading ends of the sliver as viewed in a predeterminate direction of movement or travel of the sliver from the sliver feed unit or feeder to the spinning means. The spinning means further comprise twisting means for twisting a part or portion of the fibers of the sliver conveyed by the suction means into a false-twisted yarn core. This twisted part or portion of the fibers constitutes an inner part or portion of the delivered fibers of the sliver. Outer parts or portions of the delivered sliver are supplied as so-called edge fibers by the suction means to the false-twisted yarn core for winding around the false-twisted yarn core with a pitch or helix angle which is steeper than the pitch or helix angle of the fibers of the false-twisted yarn core. Also provided are means for drawing-off or withdrawing the finished or spun yarn.
Various false-twist spinning methods or processes for producing a yarn are known in the textile arts, wherein the yarn core has the core fibers in an untwisted state and the wrapping fibers for holding the untwisted fibers together are wound therearound. Both the untwisted yarn core fibers and the wrapping fibers are staple fibers which are usually delivered by a drafting arrangement or mechanism.
A false-twist spinning method as known from German Pat. No. 2,620,118, published Nov. 18, 1976 and U.S. Pat. No. 4,183,202, granted Jan. 15, 1980, employs a false twisting nozzle and an untwisting nozzle. A sliver delivered by a drafting arrangement is divided into core fibers and edge fibers. The core fibers are false-twisted by the false twisting nozzle, which is the second nozzle as seen or considered in the direction of yarn movement, whereas the edge fibers which contact the false-twisted core are twisted by the first untwisting nozzle, again as seen or considered in the direction of yarn movement, around the false-twisted core in an opposite direction of rotation. As the false-twisted yarn core untwists, the edge fibers become looped or wound even more tightly around the yarn core in the form of wrapping or coiling fibers. Consequently, there can arise what are known as corkscrew effects in the spun yarn which can impart a certain stiffness thereto, and thus, a boardy texture or hard handle to the cloth or fabric produced from such yarn.
European Published patent application No. 0,131,170, published Jan. 16, 1985, and the essentially cognate U.S. Pat. No. 4,565,063, granted Jan. 21, 1986, discloses further prior art for fabrication of false-twist spun yarns. In this prior art method only a single twisting nozzle is used, namely the nozzle for false twisting the yarn core. A special feature of this method is that the distance between, on the one hand, the place where the edge fibers are brought into engagement with the false-twisted yarn core and, on the other hand, the nip line of the exit roll pair is such that the edge fibers are wound around the yarn core as long as their rear or trailing ends remain clamped in the nip of the exit roll pair. Consequently, the end of the individual edge fiber is wound into the so-called spinning triangle while the edge fibers are twisted around the yarn core in the direction of rotation thereof but at a much steeper pitch or helix angle, so that when the yarn core untwists into a position in which the core fibers are parallel, the edge fibers are twisted through a neutral position, in which they extend parallel to the direction of yarn conveyance, and then in an opposite twist direction. In other words, the edge fibers, if they had an S-twist before the untwisting of the yarn core, then would have a Z-twist in the finished yarn.
With this prior art technique, the edge fibers are therefore wound sufficiently tightly around the yarn core but not so tightly as to cause marked or pronounced corkscrew effects.
The disadvantage of all systems using compressed air or pneumatic twisting nozzles resides in the limitation of the speed of rotation of the air vortex or eddy by the speed of sound in air, and, therefore, of the yarn core in the twisting nozzle.
Consequently, in another known method as disclosed in German Published patent application No. 3,639,031 A1, published May 21, 1987 and the cognate U.S. Pat. No. 4,674,274, granted June 23, 1987, the edge fiber coiling nozzle was combined with a belt twister in the form of two driven crossed friction belts.
This solution of the problem obviates restriction on the twist which can be imparted to the false-twisted yarn core but does not obviate the problem of severe corkscrewing and the disadvantage of fiber guidance from the nip line or region of the drafting arrangement up to and including the belt twister.